Process of preserving potatoes in closed packages

ABSTRACT

A process for preserving foodstuffs such as potatoes in closed packages of foil packing material wherein the peeled, raw and if required sliced or diced potatoes are vacuum-packed without any included liquid and cooked or steamed and then cooled at a external pressure exceeding the internal pressure in the packing and controlled independently of the temperature, and wherein during the vacuum-packing process each potato or piece of potato is brought into direct contact with the inside of the packing material through at least a part of its surface area, preferably a third.

United States Patent Mohwinkel [4 1 Apr. 25, 1972 54] PROCESS OFPRESERVING POTATOES 3,355,304 10/1967 IN CLOSED PACKAGES 3,501,3183/1970 2,231,791 2/1941 [72] Inventor: Franz Mohwmkel, Ahlften uberSoltau, 3 190 759 6/1965 Germany [73] Assignee: Plasco Limited Company,Vaduz, FOREIGN PATENTS 0R APPLICATIONS Liechtenstein 579,098 7/1959Canada ..99/171 Nov. 20, l 3 Great Bl'ltall'l i 7] [21] App]. No.:878,418 OTHER PUBLICATIONS Related US, A li ti D AVl Publication, PotatoProcessing, Dec. 5, 1968 p. 588

v National Potato U. Conference, May 1962 p. 32. [63]Continuation-in-part of Ser. No. 804,694, Mar. 5,

1969' Primary ExaminerNorman Yudkofi- Assistant E.mminer--Martin G.Mullen {30] Foreign Application Priority Data Anomey cushman Darby andCushman June 28, 1969 Germany ..P 19 32 900.1

[57] ABSTRACT [52] US. Cl ..99/17l, 99/100 P A process for preservingfoodstuffs such as potatoes in closed [5]] 31/02 23! l/ l 2 packages offoil packing material wherein the peeled, raw and [58] held if requiredsliced or diced potatoes are vacuum-packed without any included liquidand cooked or steamed and then cooled at a external pressure exceedingthe internal pressure [56] References cued in the packing and controlledindependently of the tempera- UNITED STATES PATENTS ture, and whereinduring the vacuum-packing process each potato or piece of potato isbrought mto dlrect contact wlth 2,597,067 5/1952 Chase ..99/100 X theinside f the packing material through at least a part f its 2,609,3019/1952 Lmdsey ..99/l71 X surface area f bl a m 3,175,914 3/1965Vahlsing, Jr ..99/l00 P 3,215,539 1 1/1965 Landy ..99/221 6 Claims, 11Drawing Figures Patented April 25, 1972' 3 Sheets-Shet l he. 3 E

I VEN TOR Aw A/Z Mm/W/Mea Patented April 25, 1972 3,658,559

3 Sheets-Sheet z Patented April 25, 1972 3 Sheet-Sheet 3 IN VEN TOR Kai/v2 M0f W/A K L PROCESS OF PRESERVING POTATOES IN CLOSED PACKAGES Thisis a continuation-in-part of my co-pending application, Ser. No.804,694, filed Mar. 5, 1969.

The present invention relates to the art of preserving and sterilizingfoods and, more particularly, to a novel process for preservingfoodstuffs such as potatoes in closed packages using pressure cookers(autoclaves) or cooking receptacles, and to the packaged goods thuspreserved.

In the known processes of preserving potatoes by canning or bottlingthem in water a product is obtained which can be preserved for arelatively long period but which, as a result of being stored in apreserving liquid, deteriorates in flavor and loses valuable nutrientsubstances which are leached out by the liquid. Moreover, canning and,in particular, bottling are expensive and inconvenient and, when buying,the customer cannot see the product in the can, which is a possibledisadvantage.

The object of this invention is to remove the present disadvantages andto provide an improved process of producing preserved potatoes whichhardly differ in taste from fresh boiled potatoes and which, even in thewrapped state, afford an attractive appearance.

A further object of this invention is to provide a process of producingwell preserved potatoes which are readily usable without furthercooking, but only warming up.

Yet another object of this invention is to provide a process ofproducing a product which keeps for a relatively long period of time andwhich is neither leached out nor deteriorated in appearance andparticularly color and taste compared to the natural product.

A further object of this invention is to produce a potatoproduct whichis available to the user in packages, the quality of which he or she canjudge by eye.

Further and other objects and advantages of the invention will beapparent from the following detailed description thereof.

In my process for cooking or steaming potatoes in closed packages withthe aid of cooking autoclaves or'cooking receptacles, peeled rawpotatoes are vacuum-packed in plastics containers with the treatingtemperature of about+ 100 C. or somewhat higher, while the absolutepressure in the cooking autoclaves or cooking receptacles is keptconsiderably higher than the absolute internal pressure of the containerby supplying the latter, during the preserving treatment with steam,with so much compressed air that, at a temperamre of about 100 C., thetotal pressure in the steam space considerably exceeds the correspondingpartial pressure of the steam of l atms., or the total pressure in thecooking receptacle considerably exceeds the steam pressure correspondingto this temperature. With this process, the potatoes are vacuum-packedin plasticfoil containers without any addition of liquid and are cookedand cooled under an external pressure exceeding the internal pressure ofthe closed containers and controlled independently of the temperature.

It is an essential feature of this process that at least one part of thesurface of each potato or each piece of potato is brought into directcontact with the inside of the packing foild during the vacuum-packingprocess step.

If potatoes vacuum-packed in packages of foil material without anyliquid undergo the cooking process in autoclaves or cooking receptacles,the danger arises that if the cooking temperature is relatively high,about 120 C., or if during the cooking process, for one reason oranother, it unintentionally increases and the packaged potatoes areexposed for a longer time to a temperature of this value, incrustationand discoloration of the surface of the potatoes or pieces of potatooccurs. This leads to a considerable reduction in the quality of theproduct.

On the other hand, for practical reasons, it is desired to usetemperatures of this level for cooking the potatoes since thesetemperatures are usually used in the common canning and bottlingpreserving methods wherein the potatoes are treated with liquid, andfurthermore, the internationally accepted standard for the sterilisationeffect is based on a cooking temperature of 12 l C.

l have found that with the new process in which the potatoes are treatedwithout liquid, these high temperatures can be used provided that theform of the packing bears a certain relation to the form of the articlesof produce to be packed, namely so that during the filling andvacuum-sealing processes, one point of the surface of each individualarticle of produce comes into direct contact with the packing materialand is fixed in this position for the subsequent stages of treatment. Inthis manner, with the process according to the invention, cooking can beundertaken at any of the usual cooking temperatures. As with the knownprocesses, for each individual case the optimum conditions during thecooking stage are practically determined from the relation: cookingtemperature cooking time. In the temperature region in question, fromabout l00-l25 C. and in the respective range of the cooking period offrom about 20 minutes up to 2 hours, the height of temperature levelandthe length of period of time are in reciprocal relationship, i.e., undergenerally uniform conditions, practically uniform results are obtainedif cooking is undertaken for about 2 hours at C. or about 25 minutes at121 C.

With the method according to the invention, the external pressuresurrounding the filled packages is controlled and thus adjustedindependently of the temperature during the cooking process and thesubsequent cooling, so that it considerably exceeds the internalpressure in the package containers. By way of example, with a cookingtemperature of 121 C., at which the internal pressure in the packagescorresponds approximately to the steam pressure of the water present inthe packed potatoes, thus at about 1 atmospheric excess pressure, theexternal pressure is set at one atmosphere higher, namely at about 3atms. absolute pressure.

The arrangement according to the invention, of bringing each individualpiece of the produce to be treated into direct contact with the wall ofthe packing material, seems surprising at first, for usually a directcontact is allowed only when it is consciously desired to brown theexternal surface of the pieces of potatoes, e.g., during the preparationof roast potatoes. However according to the invention, this step has thereverse effect of avoiding browning or other chemical change at anypoints of the surface of the pieces of produce to be treated.

Having carried out thorough investigations, 1 am able to theoreticallyexplain the surprising effect which is reached with the previouslydescribed technical steps of the process according to the invention, asfollows:

When cooking or sterilising vacuum-packed potatoes or pieces of potatoeswhich are packed in foil material without any liquid, completelydifferent conditions are valid for the conduction of heat and heattransfer compared to the preserving of potatoes with liquid in cans orbottles. With the known method of preserving, the cans and bottlesfilled with the potatoes and liquid and then closed are heated from theoutside and the heat transfer within the containers takes place throughthe transition of heat via the wall of the container heated by theexternal heating medium and the liquid, generally water, to the produceenclosed in the can or bottle which is to be heated. Since the liquidmaterial, such as water, is a good conductor of heat, after a relativelyshort period of heating, the heat is equally and thoroughly distributedin the inner space of the packing container. It is known that thistransfer of heat can be speeded up by moving or tumbling the cans duringheating.

If on the other hand, potatoes are vacuum-packed in packaging containerswithout any liquid, such a type of heat transfer cannot take place.Though even then the wall of. the packing material is brought to thedesired temperature owing to its direct contact with the externalheating medium, however, since transmitting medium is missing from theinner space of the vacuum-packing, the heat can only be transferred fromthe wall of the packing material directly on to individual pieces ofproduce at those parts where the packing material is plied from theoutside is in this case onlypossible by way of packing foil 2 which issurrounded by the heating medium 3. The path which must be covered bythe heat supplied from the heating medium 3 via the packing foil 2 inorder to reach the the packed potatoes and only at those parts where thepieces of produce are in contact. This and the fact that potato itselfis a poor conductor of heat compared to water impedes the uniform heatconduction and can lead to localization of heat ing. It must be addedhere that the potatoes, particularly the uncut or comparatively largepieces, are extremely sensitive and in the case of a high orparticularly lengthy heating caramelization or burning occurs, as aresult of such a localisation of heat. It is therefore practicallyimpossible without this reduction in quality to maintain heating untilthe heat from the layers of the packed produce in direct contact withthe packing foil has passed to the produce located furthest from thepacking material towards the center of the packing and the balance ofheat has been adjusted. The outermost potatoes would burn or, if thiswere prevented, the innermost potatoes would be insufficientlysterilized.

These problems could be removed with the measures according to theinvention. It is thus unnecessary to transfer heat from one potato orpiece of potato to another; each individual piece of the produce isimmediately supplied with heat from the outer heating medium through thedirect contact between the piece and the packaging material. 1

The invention will now be explained with reference to th accompanyingdrawings which illustrate an embodiment of the packaging according tothe invention and, for comparison, a known type of packaging. I

In the drawing: FIG. 1 is a side view of a package corresponding to theprocess according to the invention; 1 .FIG. 2 is a cross-sectional viewof the package according to FIG. 1;

FIG. 3 is a plan view of FIG. 2; FIG. 4 is a plan view ofFIG. 1; FIG. 5is a cross-sectional view of 'a modifiedembodiment of the type ofpackage used with the process according to the invention; i

' FIG. 6 is a plan view of the embodiment of FIG. 5;

FIG. 7 is a cross-sectional view of an embodiment used for comparison; 1J FIG. is a plan view of the embodiment according to FIG. 7; v

FIG. 9 is a side view of another'form of comparison; FIG. 10 is across-sectional view of the embodiment according to FIG. 9; and

FIG. 11 is a cross-sectional view of the form of a large package in thecase of the process accordingto the invention.

"In' all drawings, comparable parts are provided with the same referencenumerals.

FIGS. 1 to 4 illustrate the most favourable form of package according tothe invention. Each potato la or piece of potato lb is in direct contactwith the packing material 2 which is surrounded by the external heatingmedium 3, consisting of steam or water. As is clearly seen in FIG. 2,the majority of the individual potatoes or pieces, if they are diced,have two side faces directly on thepacking material so that incross-section about a third of the surface of the packed produce 10 and1b is able to absorb the heat supplied by way of the heating medium 3and the packing foil 2. As illustrated by the arrows in FIGS. 2, 3 and4, this heat only needs to cover a relatively short path in order toreach the parts furthest away from the outer edge of the package,namelythe core 4 of the packed produce,

which enables a uniformly favourable heating to occur in a reasonabletime, whilst also taking into account the relatively poor conduction .ofheat of the potatoes.

A sufficiently unifon-n supply of heat which can be'reached in areasonable time is, as has been found, also possible with theembodiments illustrated in FIGS. 5 and 6. In the arrangement indicated,each potato 1a or piece of potato lb is not heated from two sides butfrom one side, since the side faces of each piece In and lb (in dicedform) is in contact with the a core 5 which is here located between theindividual pieces of produce adjoining the packing foil on each side isabout twice as long as with the embodiment in FIGS. 1 to 4, but as hasbeen found, can still be achieved in suitable times so that at leastwith ordinary types of potatoes, this embodiment of the processaccording to the invention illustrated in FIGS. 5 and 6 leads to veryfavorable results.

FIGS. 7 and 8 illustrate containers which have such a poor conduction ofheat that a suitable sterilization of the inner potatoes 10 or pieces ofpotatoes 1d is not possible without a severe decrease in quality. Asindicated by the arrows, the heat transferred from the heating medium 3to the packing foil 2, and from there to the potatoes 1a or pieces ofpotato lb in dirct contact with the packing, must flow not only throughone individual piece of potato 1a or lb, but must also pass from thereto an inner potato lc or piece of potato 1d, which is not in directcontact with the packing material and likewise diffuse through thisportion. The time required for this is so long, or the supply of heat sohigh that the quality of the potatoes necessary for the present purposecan no longer be main tained. Even more unfavorable are the proportionsin a large packing, with a capacity of about 3 kg, as is seen in FIGS. 9and 10. The external heating medium 3 can only directly heat surfaces ofthe packing material 2 which are small in comparison with the entiresurface of the packed potatoes and pieces of potato 1a lb lc+ 1d and theheat is only directly transferred from the packing material 2 to the fewpotatoes In or pieces of potatoes 1b lying on the outer edge 'of thelarge package. The path of heat inwardly fromthe outsideoutlined by thearrow in FIG. 10 clearly showsthat a sufficient sterilisation of theinner core zone is not possible without the outer lying potatoes 1a orpieces of potato 1b being severely burnt.

The differencebetween thisknowntype of large package according, to FIGS.9 and. I0 and thetype which must con stitute a large package whentreated in accordance with the process according to the invention, canbe seen at a glance by comparing FIG. 10 with FIG. 11. FIG. 11, likeFIG. 2, illustrates the shortpath which the heat takes during thecooking process for the fully uniform heating of the packed produce forpotatoes packed according to the invention.

Products preserved accordingto the process of my invention are able to'be stored over periods as long as 6 months or a six months withvirtually no impairment of the wholesomeness of the potatoes.

An example of materials that may be used for the plastic container 2 isa thermoplastic synthetic organic polymer such as the productcommercially marketed by Messrs. Wolff Walsrode AG, Federal Republic ofGermany, under the commercial designation COMBITHEN S PA 3/l0 K 3060SIEGEL- RANDBEUT EL.

It will be appreciated that various modifications and variations inaddition to those suggested above may be made in the process of theinvention, and accordingly it will be understood that the invention isto be limited only within the scope of the appended claims.

Having now described this invention, what is claimed is:

l. A process for cooking and preserving potatoes ina closed and sealedpackage of plastic material comprising: vacuumpacking peeled, raw andsliced or diced potatoes in said package without adding any liquid sothat there is no water or other liquid in the closed and sealed packageother than the natural juices within the potatoes therein, cooking andthen cooling said packaged potatoes at an external pressure exceedingthe internal pressure in the package, and wherein during. thevacuum-packing step each piece of potato in said 4. The process of claim1, wherein cooking by steaming is performed with a cooking temperatureof about C. at an internal pressure in the packages of about 3 atms.absolute pressure for a cooking period of about 2 hours.

5. The process defined in claim 1 wherein the package is substantiallytransparent.

6. The process defined in claim 1 and further wherein the said packagedpotatoes, after said cooking and cooling, are stored at room temperaturewithout being refrigerated.

2. The process of claim 1, wherein during the vacuum-packing processeach piece of potato is brought into direct contact with the inside ofthe packing material through at least a third of its surface area. 3.The process of claim 1, wherein cooking by steaming is performed with acooking temperature of about 121* C. at an internal pressure in thepackings of about 3 atms. absolute pressure for a cooking period ofabout 25 minutes.
 4. The process of claim 1, wherein cooking by steamingis performed with a cooking temperature of about 100* C. at an internalpressure in the packages of about 3 atms. absolute pressure for acooking period of about 2 hours.
 5. The process defined in claim 1wherein the package is substantially transparent.
 6. The process definedin claim 1 and further wherein the said packaged potatoes, after saidcooking and cooling, are stored at room temperature without beingrefrigerated.